The modern communications era has brought about a tremendous expansion of wireline and wireless networks. Computer networks, television networks, and telephony networks are experiencing an unprecedented technological expansion, fueled by consumer demand. Wireless and mobile networking technologies have addressed related consumer demands, while providing more flexibility and immediacy of information transfer.
Current and future networking technologies continue to facilitate ease of information transfer and convenience to users. In order to provide easier or faster information transfer and convenience, telecommunication industry service providers are developing improvements to existing networks. In this regard, wireless communication has become increasingly popular in recent years due, at least in part, to reductions in size and cost along with improvements in battery life and computing capacity of mobile electronic devices. As such, mobile electronic devices have become more capable, easier to use, and cheaper to obtain. Due to the now ubiquitous nature of mobile electronic devices, people of all ages and education levels are utilizing mobile terminals to communicate with other individuals or contacts, receive services and/or share information, media and other content.
Communication networks and technologies have been developed and expanded to provide robust support for mobile electronic devices. For example, the Worldwide Interoperability for Microwave Access (WiMAX), is a telecommunications technology aimed at providing wireless data over long distances in a variety of ways, from point-to-point links to full mobile cellular type access. The evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (E-UTRAN) is also currently being developed. The E-UTRAN, which is also known as Long Term Evolution (LTE) or 3.9G, is aimed at upgrading prior technologies by improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and providing better integration with other open standards.
In a typical network configuration mobile users communicate with each other via communication links maintained by the network. In this regard, for example, an originating station may typically communicate data to network devices in order for the network devices to relay the data to a target station. The quality of service (QoS) of the radio links may be managed by an entity referred to as a radio link controller (RLC). The RLC may manage QoS of each radio bearer (RB) and the transmission of data of each RB via different types of RLC modes. Some examples of modes may include a transparent mode (TM), an acknowledged mode (AM) and an unacknowledged mode (UM). Each mode may support a corresponding different QoS. For example, TM may be a mode in which no overhead is attached to an RLC service data unit (SDU) received from a higher layer when constituting a protocol data unit (PDU). As such, the RLC may pass the SDU in a transparent manner. In non-transparent modes like AM and UM, overhead is added at the RLC.
In AM, the AM RLC constitutes a PDU by adding a PDU header that includes a sequence number that can be used by the receiver to determine whether a PDU has been lost during transmission. The receiver also provides acknowledgement for PDUs received and thus re-transmission may be requested for PDUs that were not received in order to improve efforts to provide error-free data transmission via re-transmissions when necessary. Due to the potential for re-transmissions, AM may be more well suited for non-real-time packet transmissions.
UM, unlike AM, does not provide acknowledgement for PDUs received. Thus, although the receiver may still use a sequence number provided in the PDU header to determine whether any PDU has been lost, the transmitter receives no acknowledgements for PDUs transmitted and therefore does not check whether the receiver is properly receiving transmitted PDUs. Thus, once a PDU is transmitted, the PDU is typically not retransmitted. Due to the fact that UM does not provide re-transmissions of PDUs, UM may be more suitable to real-time packet transmissions such as voice over Internet protocol (VoIP), broadcast/multicast data and other real-time services. Circuit switched (CS) voice calls may be an example of a service for which UM may provide network support. In particular, CS voice over high speed packet access (HSPA) has been introduced for WCDMA (wideband code division multiple access) in order to attempt to improve frequency efficiency and battery life by mapping CS voice services on high speed uplink packet access (HSUPA) and high speed downlink packet access (HSDPA). As such, for example, a CS voice over HSPA radio access bearer (RAB) may be mapped on a UM RLC and an adaptive multi-rate (AMR) voice codec may send audio frames, for example, for each 20 ms if audio data exists or send an AMR SID (e.g., a silence frame) for each 160 ms if no audio data exists (e.g., in silent periods).
Despite the potential for utility of UM in applications such as those described above, a ciphering problem may occur when the receiver fails to receive a certain number of consecutive UM data PDUs. For example, if the receiver fails to receive more than 127 consecutive UM data PDUs, the receiver may miss the timing to increment a hyper frame number (HFN) value so that COUNT-C values in the receiver and the transmitter may fall out of synchronization. Some exemplary situations in which the ciphering problem is encountered may include cases of bad radio conditions, hard handoffs, a fallback after a hard handoff, or a fallback after an intersystem handover to GSM (global system for mobile communication) failure. In the case of CS voice over HSPA, the ciphering problem may occur if the network keeps sending UM data PDUs and the user equipment (UE) or mobile terminal of the user keeps failing to receive the UM data PDUs for a period of about 2.56 seconds in the downlink direction, or if the UE keeps sending UM data PDUs and the network keeps failing to receive the UM data PDUs for 1.28 seconds in the uplink direction.
Although recovery mechanisms currently exist for recovering from the ciphering problem in relation to TM and AM operation, there is currently no mechanism for detecting and recovering from the ciphering problem in relation to UM operation. In light of the issues discussed above, it may be desirable to provide a mechanism for improving UM capabilities with respect to the ciphering problem.